Seems to me that Hutton was quite good for the first half of the year but when it became evident the Sabres were NOT going to make the Playoffs, they went into Tank mode. That obviously impacted the Goalies' stats. By significantly upgrading the Defence and maturity from key Forwards, the Sabres should contend for the Playoffs all season long.
Hutton had an unsustainably high save percentage during their winning streak and then he and Ullmark both struggled over the course of the rest of the season. They had a terrible defensive scheme and poorly designed and executed breakouts/transition. Add in some highly inconsistent netminding and it was easy to see how they failed.
They had multiple tenders take steps back under Allen over the last few years. All of Hutton, Ullmark, Johnson, and Lehner had reverse VH issues, short-side problems holding the post, 5-hole gaps when sort of paddle-down (but not really) -- it was the same mistakes over and over again. We suspect it was what Allen was trying to teach them that was regularly a problem. Now that he's gone, perhaps they get a bounce in regards to how their netminders play, at least in their consistency.
There was no "Tank mode".